At least 10 people were killed and an unidentified number of others injured at a shooting at a center for adult education in central Sweden on Tuesday, the authorities said.

The police said they had started a “major operation” and locked down the campus in the city of Orebro, after shots were heard about 12:30 p.m. local time.

“This is an awful, exceptional incident — a nightmare,” said Roberto Eid Forest, head of the local police. “We do not think there is any terror motive behind this, but it is too early in the investigation to say.”

“We think we have the perpetrator, but we are not ruling out anything,” he added Tuesday evening.

At a news conference earlier in the day, the police said they believed that the shooter was among the wounded, but did not offer further details on a motive or the person’s identity. The shooter most likely acted alone and was not affiliated with a gang and was not known to the police, Mr. Forest said.

“We suspect one of the people in the hospital is the perpetrator,” the police said in an earlier statement posted online.

Images in Swedish news outlets earlier in the day showed dozens of police cars surrounding the center’s campus. The police locked down several other schools in the area as part of their response.

“It is a very painful day for all of Sweden,” the Swedish prime minister, Ulf Kristersson, said in a statement on social media. “Being locked in a classroom, fearing for your life, is a nightmare that no one should have to experience.”

School shootings are relatively rare in Sweden, but the country has seen an increase in violent crime in recent years. In 2022, an 18-year-old student killed two teachers in the southern city of Malmo. In 2015, Sweden was stunned when a 21-year-old man, armed with a sword, killed a teacher and a student at a school in the southwestern part of the country.

“Shocked by the terrible news from Orebro,” Nooshi Dadgostar, the leader of the opposition Left Party, said on social media. “The violence our country is going through is an abyss we must find our way out of together.”